Failure analysis of K-monel 500 (Ni–Cu–Al alloy) bolts

Abstract A bolt manufacturer used several subcontractors to fabricate K-monel 500 bolts. The completed bolts failed mechanical testing, and the manufacturer ascribed the failure to the bar stock. Testing contracted by the supplier of the bar stock showed that it met specifications. Metallographic testing described here shows that the bolts failed because of excessive grain growth and subsequent softening during heat treatment performed on the bolts after they were formed. Alternative heat treatments are discussed.